A/C struggles in hot weather

My house has dual HVAC zones, and when the weather gets really hot (upper 90s with humidity), the unit in my attic struggles to cool the upper level. The inside temp starts to creep into the upper 70s, and the unit runs non-stop. I had 2 attic fans installed a few years ago, and that helped. I noticed that my attic is insulated to R30, and I am wondering if going to say R38-R40 would make a noticeable difference with my upper unit A/C. I guess at some point there are diminishing returns on insulation.

Would it be worth the cost to get a contractor to blow in more attic insulation? If so, what would be a reasonable cost per square foot to go from R30 to R40?

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A/C struggles in hot weather

Have you had the unit properly serviced? Freon level needs checking etc etc. More insulation is better but you have to phone some contractors for prices. The ducts in the attic should be checked to make sure they are properly sealed, now is the time to do it and not when it gets HOT.

A/C struggles in hot weather

the coil on that air handler can only do 18F difference on the entering and leaving air and you need to verify that the return air is true space air and noting from the attic is being be sucked in to jack that return up.do you just have a single return grill in the 2nd floor hallway,and does it go right into the back of the air handler.then the suply ducts are they insulated flex runs with minimal elbows and turns.the charge has to be up to operating levels if anything less your tonnage is less in doing that 18F split.if your condenser is being banged by the sun that adds to the operating conditions compared to a shaded area...start with the ducts then get the charge checked. 18F air splits on the air handler(drop) as mentioned then 10F on the condenser(rise)

A/C struggles in hot weather

As recommended, I am getting the unit serviced. Meanwhile, no one has offered an opinion on the merits of increasing the insulation from R30 to R40. Would this be a worthwhile investment? Or is R30 "good enough"?

A/C struggles in hot weather

just opinion. Every little bit you can do will help. I doubt you'll really notice any difference & pay back will probably take years.. You already have R30 which is far more than most ( atleast in my area) All your duct work ,coil etc, is in a hot attic. If the duct work is metal . Your a/c has to cool all this metal down.. If I were going to insulate anything, it would be an outside wrap of the duct work & coil

A/C struggles in hot weather

Attic fans?

The air being displaced in the attic has to be replenished from somewhere. I know you have R30 but you are actually pulling air from the upper floor into the attic. You are actually adding more infiltration load.

A/C struggles in hot weather

Quote:

Originally Posted by kennelm

As recommended, I am getting the unit serviced. Meanwhile, no one has offered an opinion on the merits of increasing the insulation from R30 to R40. Would this be a worthwhile investment? Or is R30 "good enough"?

If your attic reaches a temp of 150°F, and you keep your house temp at 70°F.
Increasing from R30, to R40, lowers your heat gain by 1,000 BTUs total, on a 1500 sq ft ceiling.

Not a cost saving thing for cooling alone.
And only helps the A/C minimally.

A/C struggles in hot weather

Isn't that what the soffit vents and the end gable vents are for? As said they were designed for passive ventilation only. They are not big enough for power ventilaters,

Well, I noticed an improvement after the vents were installed. It definitely pulls that super-heated air from the attic...

Yes the attic is cooler but studies have found that your pulling around 20% of that air from the house through the attic floor. This is air that you have already paid to condition. This also could put your house in a negitive pressure which could cause health problems and unsafe conditions.

You would be much better off sealing the attic floor (remove insulation, seal and then put insulation back. Also installing a radiant barrier at the roof line will stop the infrared infiltration through the roof.